Extraction of fiber from fiber plants would allow its eventual usage. Extraction primarily involves removal of non-cellulosic material, e.g. pectin and colour-containing materials, from the fiber. This removal of non-cellulosic material is sometimes referred to as degumming. Pectin is a polysaccharide which is a polymer of galacturonic acid. Pectin is not soluble in water or acid. However, it can be removed by strong alkaline solutions like caustic soda (concentrated sodium hydroxide).
General methods for isolation of clean fibers include dew retting, water retting, and chemical and enzymatic processes, with different variations. In these methods, the glue that holds the fibers together must first be loosened (or removed altogether) by retting. In conventional retting, stalks are dew-retted by allowing them to lie in the field after cutting. These retting approaches depend on digestion of pectin by enzymes secreted by microbes thriving under favorable conditions. Although water-retting yields more uniform fiber, the process pollutes the water. Dew-retting requires anywhere from two to six weeks or more to complete, requiring the stalks to be turned at least once for highest-quality fiber. Dew-retting is thus affected by the weather, which offers no guaranty of favorable condition.
On an industrial scale, chemical scouring is common. Chemical scouring is a process that improves the water absorbancy and the whiteness of textile by removing the non-cellulosic substances from cotton, flax or other natural cellulosic fibers, thereby facilitating the subsequent dyeing and finishing processes (Sawada and Ueda. 2001; Solbak, et al. 2005; Tzanov et al., 2001). Violent, hazardous chemicals like soda ash, caustic soda and oxalic acid used in the current scouring processes cause severe environmental problems, besides a loss of fiber strength.
In the past several years, considerable attention has been paid to replacing traditional processes, e.g. chemical scouring of raw cotton and flax fabrics and retting of flax and hemp fibers, with more environmentally friendly and economically viable biotechnological processes. Enzyme retting or bioscouring involves the action of a pectinase, especially pectate lyase, with or without other enzymes like xylanase and/or cellulase. Such processes are generally known (Akin et al., 2001; Klug-Santner et al., 2006; Ossola and Galante. 2004; Ouajai and Shanks. 2005; Sawada and Ueda. 2001; Solbak, et al. 2005; Tzanov et al., 2001). Pectate lyases specifically remove non-cellulosic material without damaging the cellulose backbone of the fiber. Further, enzymes used for bioscouring reduce environmental pollution (Solbak, et al. 2005). Pectate lyases widely exist in bacteria (Berensmeier et al. 2004; Klug-Santner, et al. 2006; Kluskens, et al. 2003) and fungi (Benen et al. 2000; Huertas-Gonzalez et al. 1999).
Other examples of prior art include U.S. Pat. No. 6,124,127, WO 2001/079440, WO 2000/042152 and WO 2006/0089283. These documents disclose various pectate lyases for use in detergents or textile processing.
Despite the interest in pectate lyases for use in bioscouring processes, many pectate lyases currently in use suffer from a lack of scouring efficiency. Lack of scouring efficiency can arise from thermal instability and/or low enzymatic activity of the pectate lyase. Thermal instability results in reduction of activity over time due to thermally induced changes in enzyme conformation. Higher temperatures accelerate reduction in activity. Low enzymatic activity limits the rate at which scouring can occur. Scouring efficiency can be increased by using pectate lyases having increased thermostability and/or enzymatic activity.
Thus, there is a need for enzymes, particularly pectate lyases, having increased thermostability and/or enzymatic activity.